From: Jim Mattson <jmattson@google.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: kvm list <kvm@vger.kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Wanpeng Li <wanpengli@tencent.com>,
Like Xu <like.xu@linux.intel.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] KVM: SVM: drop MSR_IA32_PERF_CAPABILITIES from emulated MSRs
Date: Tue, 16 Jun 2020 09:52:54 -0700 [thread overview]
Message-ID: <CALMp9eQ1qe4w5FojzgsUHKpD=zXqen_D6bBg4-vfHa03BdomGA@mail.gmail.com> (raw)
In-Reply-To: <87366vhscx.fsf@vitty.brq.redhat.com>
On Tue, Jun 16, 2020 at 9:45 AM Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>
> Jim Mattson <jmattson@google.com> writes:
>
> > On Tue, Jun 16, 2020 at 9:14 AM Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
> >>
> >> state_test/smm_test selftests are failing on AMD with:
> >> "Unexpected result from KVM_GET_MSRS, r: 51 (failed MSR was 0x345)"
> >>
> >> MSR_IA32_PERF_CAPABILITIES is an emulated MSR indeed but only on Intel,
> >> make svm_has_emulated_msr() skip it so it is not returned by
> >> KVM_GET_MSR_INDEX_LIST.
> >
> > Do we need to support this MSR under SVM for cross-vendor migration?
> > Or, have we given up on that?
>
> To be honest I'm not sure about the status of cross-vendor migration in
> general and PMU implications in particular, hope Paolo/Sean can shed
> some light. In this particular case my shallow understanding is that
> MSR_IA32_PERF_CAPABILITIES has only one known feature bit which unlocks
> an MSR range with additional counters. If the feature bit is not set
> this, I guess, can easily be migrated (basically, let's allow writing
> '0' there on AMD and return '0' on read). But what if the feature was
> enabled? We'll have to support the new MSR range and do something with
> it after migration (run intel_pmu in fully emulated mode?).
>
> Anyway, the immediate issue I'm trying to fix here is: whatever is
> returned by KVM_GET_MSR_INDEX_LIST can be successfully queried with
> KVM_GET_MSRS as some userspaces count on that.
That's a nice property. Is it documented somewhere?
Reviewed-by: Jim Mattson <jmattson@google.com>
next prev parent reply other threads:[~2020-06-16 16:53 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-16 16:14 [PATCH] KVM: SVM: drop MSR_IA32_PERF_CAPABILITIES from emulated MSRs Vitaly Kuznetsov
2020-06-16 16:24 ` Jim Mattson
2020-06-16 16:45 ` Vitaly Kuznetsov
2020-06-16 16:52 ` Jim Mattson [this message]
2020-06-17 11:38 ` Vitaly Kuznetsov
2020-06-17 16:47 ` Jim Mattson
2020-06-17 17:17 ` Paolo Bonzini
2020-06-18 11:08 ` Vitaly Kuznetsov
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